User Tools
This is an old revision of the document!
Alternators can be used as motors.
How To
Get an alternator from a junkyard (or pay for a new one on ebay, rockauto.com, etc.)
(David Ortiz-Grob) First stop: get that 1500w motor controller that’s like $34 (Jared McNeil)
this one: https://www.ebay.com/.../48V-DC-1500W.../252876629480… EBAY.COM 48V DC 1500W Brushless Motor Controller For E-bike Scooter…
(Craig Byrne) Is there an agreed upon field winding voltage range yet? Or if it needs to be dynamic depending on throttle? (Jared McNeil) the way i understand it is that field current is more important than field voltage, and that it should be right around 4 Amps continually from startup all the way up until your max speed. THEN it is optionally dynamic (but only in the lessening direction) to further your top-end.
Jared McNeil we ran with a 12V4A field coil on a bench test with success Iacona Andrew What do you use to make the field
Craig Byrne Basically, take the cap off an alternator and remove the diode pack., you'll either find 3 wires of 6 wires on the outer windings. If it's 6 make them into 3 consecutive pairs. Then take apart the part where the brushes contact the “commutator” you'll need to apply voltage to this to make the the the shaft an electromagnet. This replaces the permanent magnet in other brushless motors.
Jared McNeil this isn't the best video in the world but it goes over a bit about how to make those changes: https://www.youtube.com/watch?v=IKqy3rRWJQE
YOUTUBE.COM Converting a Car Alternator into a Go Kart Motor
Iacona Andrew I watched it seems to skip a lot of things
Jared McNeil yeah there's some more content i found about it when i was researching about how to do it also and idk if i can find it again
Iacona Andrew Also does the size matter? Car, truck etc
David Ortiz-Grob David Ortiz-Grob Bigger is better obvs but there’s no straightforward way to convert the rated generation voltage and current into usable motor power
(Not entirely true. The big alternators on Phantom ICT seem to draw a lot of current just spinning themselves with no load. Whereas the smaller ones on Phantom 48 seem to have a lower current draw. This matters due to the fuse limit.)
Murray Hersh Murray Hersh Just as a heads up on the $30 eBay controller. It's generally a great controller however it does seem to be limited in terms of maximum output frequency.
We could figure out how well it will work if we know the kv of the alternator (under various field currents) as well as the number of poles.
IaconaAndrew What would be the better speed controller for this project? On a budget of course
Murray Hersh Murray Hersh IaconaAndrew The eBay controller actually should work pretty well especially for a budget build. I'm generally impressed by the controller, especially for $30. It's biggest limitation is output frequency, however with the data Marshall Scholz posted a…See More
Murray Hersh Murray Hersh Okay here is some data courtesy of Marshall Scholz:
All duty cycle at 95%
Actual voltage is correct. Batt was discharged
Rotor current: 0.93a Rotor watt: 2w Vbat: 45.7v Ibat: 4.52 Imotor: 4.76 Watt@noLoad: 207w erpm@no load: 38338.0
Rotor current: 1.5a Rotor watt: 2.9×1.5 = 4.35w Vbat: 45.7v Ibat: 4.74 Imotor: 4.99 Watt@noLoad: 216w erpm@no load: 27448.0
Rotor current: 2.0a Rotor watt: 3.9×2.0=7.8 w Vbat: 45.7v Ibat: 5.05 Imotor: 5.31 Watt@noLoad: 230w erpm@no load: 23005.0
Rotor current: 3.0a Rotor watt: 5.9×3.0=17.7w Vbat: 45.7v Ibat: 5.85 Imotor: 6.15 Watt@noLoad: 267w erpm@no load: 19293.0
In short the output frequency is a little high at the low field current side of things, but should work under the higher field current values with the standard eBay “1500w” controller. I would recommend sensorless honestly.
Marshall Scholz A 100+a alternator is probably ideal. I Use one of these https://ebay.com/itm/172787419292?ul_noapp=true DC-DC Buck Converter Step Down Regulator 60V 48V 36V 24V 12V to 19V 14V 9V 6V 3V
To supply my rotor current. Since it is resistive and doesn't recieve a changing feild you. Can use cc or cv to power it I use 3a when I'm not dynamically controlling the feild on my alternator. I suggest having an easy to reach pot that will control feild current if you don't do it dynamically. It should adjust between 1-5a
Andrew Davis FYI. Wear safety glasses. I got one of these and was adjusting the output voltage an it blew the capacitors. Albeit, I was adjusting the regulator no load, which i don't think should matter, but whatever safety first!
IaconaAndrew The one question that jury still seems to be out on is what alterntor will work best? Truck, SUV, car ? I ve learned bigger is not always better
Pole Guy It seems the GM alternators on Phantom 48 (which are smaller) seem to draw less current at full speed. That's good. The bigger ones used on Phantom ICT draw more current at high speed. They work, but maybe not so good.
Also, belt drive works great, but maybe not so well with sensorless controllers, because there is no slop (from a chain) so the motor controller has trouble starting with the full load applied immediately as it can't figure out it's position without drawing too much current.
